windowfunction.m

Signal and Sytem Using Matlab 书的源代码 注释详尽 m文件

% Example 10.11
% 介绍矩形窗，hamming窗和hanning窗
Wc = .4;
N = 41;   % length of filter
m = (N-1)/2;       % phase shift
n = 0:2*m+10;
n_m = n-m + ((n-m)==0)*eps;  % to avoid dividing by zero，          巧巧巧巧巧巧！！！
h = sin(Wc*(n_m))/pi./(n_m);

% use the rectangular window first
w = [ones(1,N) zeros(1,length(n)-N)];
hd = h.*w;
clf % clears current figure
subplot(211),stem(n,hd)
title('Figure 10.24:  Rectangular Window')
xlabel('n')
ylabel('hd[n]')
W = -pi:2*pi/500:pi;
Hd1 = freqz(hd,1,W);
subplot(212),plot(W,abs(Hd1));
axis([-pi pi 0 1.5])
ylabel('|Hd|')
xlabel('\Omega')

% mark text on graph
hold on
plot([-.37 .37],[.707 .707],'--r',[-.37 -.37],[0 .707],'--r',...
   [.37 .37],[0 .707],'--r',[.35 .5],[1.071 1.071],'r',[.35 .5],[0.971 .971],'r',...
   [.16 .19],[.105 .105],'r');
text(.62,1.03,'Passband ripple is 0.1')
text(.47,.707,'0.707')
text(.62,.2,'Stopband ripple is 0.104')
hold off
pause

% redo with the Hanning window
w = [0 hanning(N-2)' zeros(1,length(n)-N+1)];    % alternate expression 
hd = h.*w;
subplot(211),stem(n,hd)
title('Figure 10.25: Hanning Window')
xlabel('n')
ylabel('hd[n]')
W = -pi:2*pi/500:pi;
Hd2 = freqz(hd,1,W);
subplot(212),plot(W,abs(Hd2));
axis([-pi pi 0 1.5])
ylabel('|Hd|')
xlabel('\Omega')
axis([-pi pi 0 1.5])

% mark text on graph
hold on
plot([-.33 .33],[.707 .707],'--r',[-.33 -.33],[0 .707],'--r',...
   [.33 .33],[0 .707],'--r');
text(.62,1.03,'Passband ripple is 0.005')
text(.47,.707,'0.707')
text(.62,.2,'Stopband ripple is 0.007')
hold off
pause

% finally, use the Hamming window
w = [hanning(N)' zeros(1,length(n)-N)];
hd = h.*w;
subplot(211),stem(n,hd)
title('Figure 10.26: Hamming Window')
xlabel('n')
ylabel('hd[n]')
W = -pi:2*pi/500:pi;
Hd3 = freqz(hd,1,W);
subplot(212),plot(W,abs(Hd3));
axis([-pi pi 0 1.5])
ylabel('|Hd|')
xlabel('\Omega')
hold on
plot([-.34 .34],[.707 .707],'--r',[-.34 -.34],[0 .707],'--r',...
   [.34 .34],[0 .707],'--r');
text(.62,1.03,'Passband ripple is 0.007')
text(.47,.707,'0.707')
text(.62,.2,'Stopband ripple is 0.006')
hold off
subplot(111)